1. Field of the Invention
The present invention relates to an electromechanical pulse generator for digital voltage control in an electronic apparatus, preferably a microelectronic apparatus, such as volume control in a hearing aid.
2. The Prior Art
Microelectronic devices without digital voltage control for volume control in hearing aids are disclosed in e.g. DK-C-134,876 and DK-A-1229/89 which relate to volume control devices in hearing aids by use of a potentiometer path or a self-aligning miniature converter, respectively. However, the use of digital electronics is particularly desirable in microelectronic hearing aids as it allows better results to be obtained than the hitherto non-digitally controlled devices. Thus, there is a need for a voltage control device which is immediately applicable within the digital electronics field and which allows a very accurate adjustment of the parameters of a hearing aid, thus furthermore making the apparatus user friendly.
Electromechanical pulse generators far digital voltage control are known from e.g. radio and television sets, in which, however, such pulse generators are provided with components of an optical, magnetic or similar character. Thus, a digital voltage control based on the light/shadow effect in an optical component incorporated in the equipment is known from e.g. the electronic equipment of radios. Due to the size of such constituent parts these electromechanical pulse generators are obviously not suitable as parts of a microelectronic hearing aid in which the total outer dimensions of the components are to be in the magnitude of 3-4 mm. In Applicant's earlier patent application DK-A-1838/90 it has been attempted to minimize equipment of this type for microelectronic use by use of an electromechanical pulse generator. However it has turned out to be relatively difficult and complicated to manufacture and mount the pulse generator due to its relatively large number of vulnerable single components of very small size as well as the relatively large possibilities of functional errors arising during use of the pulse generator due to the complex cooperation between the single components.
U.S. Pat. No. 4,282,415 discloses another pulse generator of the said type which is also suitable for minimization. This pulse generator is i.a. characterized by having two simple switch sets which are placed symmetrically and which work in the same manner for closing an electric circuit using an impact effect, as a resilient contact member of the individual switch set is brought to abut against a fixed contact member of the switch set. However, in this construction the contact impact may have an unfavourable effect in connection with the electric circuit as the impact may produce undesired multiple activations of the circuit merely by turning of the rotor of the pulse generator a single step.
Finally, WO 89/12904 discloses a mechanical pulse generator likewise suitable for minimization. This pulse generator has a rotatable crown with internal toothing in which a cam on an oscillating sleeve abutting on a spring element engages. Each of the two ends of the spring element moves, in function of the chosen direction of rotation, between two contacts of one of two pairs of contacts while a contact pin mechanically pretensions the spring element and hence the oscillating sleeve accordingly. The mode of function of this pulse generator is entirely depending on the double function of the spring element acting both as a pretension of the oscillating sleeve and as a contact spring between the contact pin and each pair of contacts, respectively. This mode of function involves a mounting of the spring element and the two pins of contacts partly outside the circumference of the rotatable crown which, however, is detrimental to a minimization of the construction down to dimensions acceptable to the use of the generator as part of a microelectronic hearing aid. Further, the double function of the spring element demands a spring characteristic which may be difficult to obtain when minimizing the spring element further down to the desired use in a hearing aid.